146 lines
4.8 KiB
C
146 lines
4.8 KiB
C
/*
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* Cogl
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*
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* An object oriented GL/GLES Abstraction/Utility Layer
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*
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* Copyright (C) 2010 Intel Corporation.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library. If not, see <http://www.gnu.org/licenses/>.
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*
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*
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*
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* Authors:
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* Robert Bragg <robert@linux.intel.com>
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*/
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#if !defined(__COGL_H_INSIDE__) && !defined(COGL_COMPILATION)
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#error "Only <cogl/cogl.h> can be included directly."
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#endif
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#ifndef __COGL_INDICES_H__
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#define __COGL_INDICES_H__
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/* We forward declare the CoglIndices type here to avoid some circular
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* dependency issues with the following headers.
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*/
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typedef struct _CoglIndices CoglIndices;
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#include <cogl/cogl-index-buffer.h>
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COGL_BEGIN_DECLS
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/**
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* SECTION:cogl-indices
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* @short_description: Describe vertex indices stored in a #CoglIndexBuffer.
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*
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* Indices allow you to avoid duplicating vertices in your vertex data
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* by virtualizing your data and instead providing a sequence of index
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* values that tell the GPU which data should be used for each vertex.
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*
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* If the GPU is given a sequence of indices it doesn't simply walk
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* through each vertex of your data in order it will instead walk
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* through the indices which can provide random access to the
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* underlying data.
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*
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* Since it's very common to have duplicate vertices when describing a
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* shape as a list of triangles it can often be a significant space
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* saving to describe geometry using indices. Reducing the size of
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* your models can make it cheaper to map them into the GPU by
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* reducing the demand on memory bandwidth and may help to make better
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* use of your GPUs internal vertex caching.
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*
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* For example, to describe a quadrilateral as 2 triangles for the GPU
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* you could either provide data with 6 vertices or instead with
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* indices you can provide vertex data for just 4 vertices and an
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* index buffer that specfies the 6 vertices by indexing the shared
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* vertices multiple times.
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*
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* |[
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* CoglVertex2f quad_vertices[] = {
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* {x0, y0}, //0 = top left
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* {x1, y1}, //1 = bottom left
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* {x2, y2}, //2 = bottom right
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* {x3, y3}, //3 = top right
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* };
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* //tell the gpu how to interpret the quad as 2 triangles...
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* unsigned char indices[] = {0, 1, 2, 0, 2, 3};
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* ]|
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*
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* Even in the above illustration we see a saving of 10bytes for one
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* quad compared to having data for 6 vertices and no indices but if
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* you need to draw 100s or 1000s of quads then its really quite
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* significant.
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*
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* Something else to consider is that often indices can be defined
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* once and remain static while the vertex data may change for
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* animations perhaps. That means you may be able to ignore the
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* negligable cost of mapping your indices into the GPU if they don't
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* ever change.
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*
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* The above illustration is actually a good example of static indices
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* because it's really common that developers have quad mesh data that
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* they need to display and we know exactly what that indices array
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* needs to look like depending on the number of quads that need to be
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* drawn. It doesn't matter how the quads might be animated and
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* changed the indices will remain the same. Cogl even has a utility
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* (cogl_get_rectangle_indices()) to get access to re-useable indices
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* for drawing quads as above.
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*/
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CoglIndices *
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cogl_indices_new (CoglContext *context,
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CoglIndicesType type,
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const void *indices_data,
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int n_indices);
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CoglIndices *
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cogl_indices_new_for_buffer (CoglIndicesType type,
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CoglIndexBuffer *buffer,
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size_t offset);
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CoglIndexBuffer *
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cogl_indices_get_buffer (CoglIndices *indices);
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CoglIndicesType
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cogl_indices_get_type (CoglIndices *indices);
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size_t
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cogl_indices_get_offset (CoglIndices *indices);
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void
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cogl_indices_set_offset (CoglIndices *indices,
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size_t offset);
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CoglIndices *
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cogl_get_rectangle_indices (CoglContext *context, int n_rectangles);
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/**
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* cogl_is_indices:
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* @object: A #CoglObject pointer
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*
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* Gets whether the given object references a #CoglIndices.
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*
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* Return value: %TRUE if the object references a #CoglIndices
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* and %FALSE otherwise.
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* Since: 1.10
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* Stability: unstable
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*/
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CoglBool
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cogl_is_indices (void *object);
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COGL_END_DECLS
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#endif /* __COGL_INDICES_H__ */
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